PROJECT SUMMARY/ABSTRACT This application will foster the development of an independent research career focused on leveraging innovative treatment formats and techniques to target difficult-to-treat and difficult-to-reach child populations. The PI will gain the necessary skills and research training to conduct rigorous clinical evaluations from an experimental therapeutics framework for youth populations that present with unique obstacles to care, such as complex symptom presentations and/or lack of accessibility to quality care. Selective mutism (SM) is one such complex child disorder that requires specialized care that is not readily available for most youth in need. SM is an anxiety disorder characterized by an inability to speak in certain social situations, despite ability to speak in familiar situations. Despite its low prevalence, SM results in severe impairment in children's social and academic functioning; because most affected children fail to speak in school, they are often insufficiently evaluated for appropriate academic services, and do not get their day-to- day needs met in the classroom. As a low base-rate disorder, expert care for SM is not broadly accessible, and the vast majority of affected children do not receive appropriate services. To address problems of access to quality care for many low base rate disorders, expert providers are increasingly offering intensive treatment options, in which individuals travel from across the world for brief (e.g., 1 week) periods of all-day sessions in treatments not offered, or not offered with similar quality and competency, in the patient's local community. Despite tremendous clinical advances in the development of group intensive behavior therapy formats for the treatment of SM, to date research has not evaluated intensive treatments for SM in a controlled trial. The project at the center of this NRSA training grant entails a pilot waitlist controlled trial evaluating a one-week group intensive behavior therapy in a diverse population of children SM (N=30) delivered over the summer. Youth will be randomized to either immediate SM intensive group behavior therapy (IGBT), or to a waitlist control (WL). Aim 1 will examine feasibility of and parental satisfaction with the program by examining dropout and daily attendance rates, standardized consumer satisfaction and barriers to treatment participation measures, and costs incurred as a result of participation in the program. Aim 2 will examine reductions in SM symptoms (as well as overall anxiety and functioning) across the two conditions after one week and potential predictors of treatment response. Aim 3 will examine maintenance of treatment response by evaluating whether or not the intensive group treatment program improves children's SM symptoms (as well as overall anxiety and academic functioning) across the two groups in the classroom 8 weeks into the following school year. Finally exploratory Aim 4 will examine individual differences in treatment response related to cultural and sociodemographic factors.